The study of sign languages offers a unique opportunity for insight into the nature of neural mechanisms for language, since sign languages utilize a transmission modality different from that of spoken languages. To understand the extent to which neural mechanisms for language are modality independent, and the extent to which they are modality-bound, we naturally turn to sign languages because through their study we can begin to solve the problem of brain organization for language in general. We link our ability to create digital records of the spatiotemporal patterns of signing with theoretically driven linguistic analyses of sign language breakdown and with psychophysical studies of motion processing in brain-lesioned signers in four series of studies. Brain Function for Sign Language. We investigate the sign language capacities of deaf signers who have unilateral lesions in either the left or right cerebral hemisphere in order to uncover the nature of brain organization for a visual-gestural language. In conjunction with linguistic analyses of signing deficits and standardized aphasia assessments, we bring to bear theoretically-driven tests for processing linguistic structure in sign language. In addition, we begin investigating the cortical representation of the processes underlying reading in deaf signers. Dynamic Visuo-Motor Representations. We directly compare the linguistic manipulation of spatial loci by brain-lesioned signers with their capacities for manipulating these same loci when they function nonlinguistically. In so doing, we investigate whether there am differing mental representations of space depending upon the function subserved, and whether the brain honors these functional distinctions. Specialization for Rapid Temporal Analysis. Studies with deaf signers, for whom language processing relies on the perception of visually changing stimuli, will help clarify the role of left hemisphere specialization in temporal analysis and language processing. We investigate capacities for rapid temporal analysis in brain-lesioned signers and relate such function to patterns of hemispheric specialization for signed and spoken language. Specialization for Non-Language Motion and Spatial Processing. In order to understand brain organization for sign language processing and for its perceptual substrate, we tease apart perceptual from linguistic deficits in brain-lesioned signers in ways that should also provide a new perspective on brain function for language and for dynamic events. We extend the investigation of cerebral specialization in deaf signers for nonlanguage spatial processing to the challenging and revealing domain of motion processing.